As is known, many food products, such as fruit juice, pasteurized or UHT (ultra-high-temperature treated) milk, wine, tomato sauce, etc., are sold in packages made of sterilized packaging material.
A typical example of this type of package is the parallelepiped-shaped package for liquid or pourable food products known as Tetra Brik Aseptic (registered trademark), which is made by folding and sealing laminated strip packaging material.
The packaging material has a multilayer structure substantially comprising a base layer for stiffness and strength, which may comprise a layer of fibrous material, e.g. paper, or of mineral-filled polypropylene material; and a number of layers of heat-seal plastic material, e.g. polyethylene film, covering both sides of the base layer.
In the case of aseptic packages for long-storage products, such as UHT milk, the packaging material also comprises a layer of gas- and light-barrier material, e.g. aluminium foil or ethyl vinyl alcohol (EVOH), which is superimposed on a layer of heat-seal plastic material, and is in turn covered with another layer of heat-seal plastic material forming the inner face of the package eventually contacting the food product.
As is known, packages of this sort are produced on fully automatic packaging machines, on which a continuous tube is formed from the web-fed packaging material; the web of packaging material is sterilized on the packaging machine, e.g. by applying a chemical sterilizing agent, such as a hydrogen peroxide solution, which, once sterilization is completed, is removed from the surfaces of the packaging material, e.g. evaporated by heating; and the web of packaging material so sterilized is maintained in a closed, sterile environment, and is folded and sealed longitudinally to form a vertical tube.
The tube is filled continuously downwards with the sterilized or sterile-processed food product, and is sealed and then cut along equally spaced cross sections to form pillow packs, which are then fed to a folding unit to form the finished packages.
More specifically, the pillow packs substantially comprise a main portion, and opposite top and bottom end portions tapering from main portions towards respective top and bottom sealing bands which extend substantially orthogonal to the axis of the pack. In detail, each end portion is defined by a pair of respective trapezoidal walls which extend between main portion of the pack and the relative sealing band.
Each pillow pack also comprises, for each top and bottom end portion, an elongated substantially rectangular fin projecting from respective sealing bands; and a pair of substantially triangular flaps projecting from opposite sides of relative end portion and defined by respective trapezoidal walls.
The end portions are pressed towards each other by the folding unit to form flat opposite end walls of the pack, while at the same time folding the flaps of the top portion onto respective lateral walls of the main portion and the flaps of the bottom portion onto the bottom sealing band.
The layout of the packaging machine requires that the folded packages are outputted, at an end station, along a first direction and in a first sense.
However, the layout of the folding unit is such that the folding unit outputs the folded packages along a second direction parallel to and staggered from the first direction, and in a second sense opposite to the first sense.
As a consequence, the packaging machine comprises a transfer device which is arranged downstream from the folding unit, and is adapted to convey the folded packages along an arch of 180 degrees which extends between the first and the second direction.
In particular, the known transfer devices substantially comprise:                a frame;        a looped chain conveyor which comprises a work branch and a return branch; and        a top and a bottom full idle disks counter-rotating about a common axis, and adapted to support the chain conveyor relative to the frame.        
The work branch of the chain comprises, in turn:                an inlet rectilinear portion which is fed with the folded packages from the output station of the folding unit;        a curved intermediate portion shaped as an arch of 180 degrees which has a centre on the axis of the disk and is supported by the top disk; and        an outlet rectilinear portion which defines the end station of the packaging machine.        
The return branch is shaped as the work branch.
In particular, folded packages move along the inlet rectilinear portion in the second sense, opposite to the first sense, and move along the outlet rectilinear portion in the first sense.
Furthermore, the curved portions of the work and return branch are supported by the peripheral regions of first halves of top and bottom disk respectively. The second halves of the disks do not cooperate with the chain conveyor.
The top and bottom disks are also supported by the fixed frame at their rotation axis.
The Applicant has found that there is the risk that, as moving along the curved portion of the transporting, the packages fall over the top disk, for example because the flaps are not perfectly sealed and, therefore, packages are unstable.
Moreover, the fallen packages could stop along the curved portion and cause the fall of further packages, thus determining the stop of the transfer device and, therefore, of the whole packaging machine.
A need is felt within industry to avoid that the fallen packages could interfere with the correct operation of the transfer device and, therefore, of the whole packaging machine.